ON NERVE-EXCITATION BY THE NERVE-CURRENT. 129 



original method by metallic closure of the circuit, and to make 

 use of some arrangement providing for equal rapidity of closure 

 and opening. And with this one must naturally be most careful as 

 to the electrical uniformity of the unpolarisable electrodes, since 

 any nerve that will react to its own current, will also be extra- 

 ordinarily sensitive to the weakest additional current, if the latter 

 should be in the same direction as the former in the interpolar 

 region. Closure, by means of a liquid or by a conducting cushion, 

 cannot, at any rate by hand, be performed with sufficient uniformity, 

 and if the contractions are not very strong, one obtains, in spite of 

 the greatest practicable uniformity of speed in raising and lowering 

 the liquid which completes the circuit, a succession of contractions 

 of very different strengths. 



Excitable preparations gave me strong make- and break -contrac- 

 tions even when the portion of nerve between the blocks of clay was as 

 much as one centimeter long, and in one case I still obtained make- 

 contractions when it reached a length of 25 millimeters. I have not 

 closely examined the conditions of the appearance or predominance 

 of the break-contraction. 



I must not, however, omit to mention that this break-contraction, 

 if one admits certain assumptions concerning the so-called internal 

 closure of the nerve-current, is to be regarded, not as a proper opening- 

 contraction, but as a contraction due to the closing of the nerve-current. 



Since it is possible, in the above-described manner, to obtain on 

 a single preparation a long series of closing- and opening-contrac- 

 tions, all that is necessary in order to tetanise the nerve is to make 

 the closures and openings succeed one another with sufficient rapidity 

 just as in the case of a battery-current. Kiihne used for this 

 purpose a vibrating mercury key. I have considered it advisable 

 to avoid the use of any metal in this experiment, partly in order to 

 dispense with the testing of electrodes by the galvanometer, partly 

 in order to demonstrate a ' tetanus without metals.' To this end I 

 fixed the cushion which serves to complete the circuit in du Bois- 

 Reymond's experiment, to the end of a rod which could be made 

 to vibrate, so that the cushion could, just like the hammer of 

 Heidenhain's tetanomotor, be applied to and removed from the 

 blocks of clay in a rapid rhythm. At first, I used for this purpose 

 a large Neef s hammer, which sometimes gave me a very strong 

 tetanus, but often failed, because the amplitude of movement of the 

 cushion was too small, so that threads of fluid between it and the 

 blocks of clay prevented the circuit from being broken. I eventually 



